SuperCDMS From Soudan to SNOLAB Wolfgang Rau Queen’s University

Cooper Radius Velocity Expected (Kepler) Observed Zwicky Luminous Matter (< 1 %) Ordinary Matter (~ 4 %) CMB Dark Matter 2W. Rau – IPP AGM 2014

Predicted by SUSY: Neutralino Universal extra dimensions: Kaluza-Klein particles WIMP Here, but not yet observed in nature: Weakly interacting Large scale structure of the Universe: Slowly moving (‘cold’) Not observed in accelerator experiments: Massive (Weakly Interacting Massive Particle) Dark Matter Interaction with ordinary matter: Nuclear Recoils (most backgrounds: electron recoils) 3W. Rau – IPP AGM 2014

Phonon energy [keV] Ionization energy [keV eeq] Nuclear recoils from neutrons Electron recoils from β’s and γ’s Thermal coupling Thermal bath Phonon sensor Target e n Phonon signal (single crystal): measures energy deposition Ionization signal (semiconductor): quenched for nuclear recoils (lower signal efficiency) Combination: efficient rejection of electron recoil background Phonon signal Charge signal Electron recoilNuclear recoil SuperCDMS Technology 4W. Rau – IPP AGM 2014

+ - - In Vacuum In Matter Electron gains kinetic energy (E = q · V  1 eV for 1 V potential) Deposited energy in crystal lattice: Neganov-Luke phonons  V, # charges Luke phonons mix charge and phonon signal  reduced discrimination Apply high voltage  large final phonon signal, measures charge!! ER much more amplified than NR  gain in threshold; dilute background from ER Neganov-Luke Phonons 5W. Rau – IPP AGM 2014

SUF, 10 mwe Soudan, 2000 mwe SNOLAB, 6000 mwe SUF 6 detectors 1 kg Ge (30 kgd )  < 3.5e-42 cm 2 SUF 6 detectors 1 kg Ge (30 kgd )  < 3.5e-42 cm CDMS Soudan 30 detectors ~4 kg Ge (400 kgd)  < 2e-44 cm 2 Soudan 15 (bigger) detectors ~9 kg Ge (~2500 kgd)  < 3e-45 cm ? SNOLAB O (100) detectors ~100 kg Ge / ~10 kg Si   e-46 cm 2 exposures are after all cuts! CDMS History 6W. Rau – IPP AGM 2014

SuperCDMS Collaboration California Institute of Technology CNRS/LPN Fermi National Accelerator Laboratory Massachusetts Institute of Technology PNNL Queen’s University Santa Clara University SLAC/KIPAC Southern Methodist University Stanford University Syracuse University Texas A&M Universidad Atónoma de Madrid University of British Columbia University of California, Berkeley University of Colorado Denver University of Evansville University of Florida University of Minnesota University of South Dakota 7W. Rau – IPP AGM 2014

Basic configuration +2 V0 V -2 V0 V Electric field calculation Implementation Germanium single crystals (620 g modules) Thermal readout: superconducting phase transition sensor (TES); T c = 50 – 100 mK Charge readout: Al electrode; interleaved with phonon sensors Low bias voltage (4 V) in regular operation One detector: ~70 V for some time CDMSlite configuration 0 V -69 V 8W. Rau – IPP AGM 2014

Implementation (CDMS setup) Stack detectors (3) to mount (“tower”) 5 towers deployed in cryostat (~9 kg Ge) Shielded with PE (for neutrons), Pb (gammas) and muon veto (cosmic radiation) Located at Soudan Underground Lab (Minnesota) to shield from cosmic radiation 9W. Rau – IPP AGM 2014

Surface events 210 Pb source 65,000 betas 0 events leakage 15,000 surface NRs Trigger Efficiency (good detector) Total Phonon Energy [keV] Events per bin Recoil Energy [keVee] 10.3 keV (Ge) cosmogenic activation Sample of low background gamma data Detector Performance 10W. Rau – IPP AGM 2014

Past Analysis Approaches “Classic” CDMS approach: minimize expected BG (<1 for data set under analysis)  threshold ~10 keV (E recoil : use Q signal for Luke correction) Low-threshold extension: strongly rising WIMP spectrum at low E  improved sensitivity in spite of BG (no surface event discrimination; E NR : Luke correction based on mean yield) CMDSlite: no discrimination, but even lower threshold; BG diluted (E NR : based on Lindhard model) ~100 kgd after cuts ~200 kgd after cuts ~6 kgd after cuts 11W. Rau – IPP AGM 2014

CRESST 2011 CDMS Si B8B DAMA 2000 CDMS 2010 CDMS low threshold 2011 XENON 10 S2 (2011) EDELWEISS II 2011 CDMS Si 2013 PICASSO 2012 XENON CoGeNT LUX 2013 Results – before 2014 CDMSlite W. Rau – IPP AGM 2014

SuperCDMS Soudan – Latest Data Low-threshold method, but now with: Surface event rejection with charge signal (interleaved electrodes) AND phonon signal (sensors on top and bottom!) Edge event rejection with charge signal (was available in CDMS) AND phonon signal (new sensor layout) New Analysis method for improved efficiency (Boosted Decision Tree) Background Model to train BDT (cosmogenics, 210 Pb chain): MC to distributions; use scaled pulses + real noise to generate `events’ (gammas for BG, neutrons for signal) Optimize tree for different WIMP masses (5, 7, 10, 15 GeV/c 2 ) BG model only for BDT training; efficiency measured with neutrons Data Quality Trigger Efficiency All before BDT (e.g. singles, veto, charge fid. vol.) BDT (phonon and charge ampl., phonon fiducial volume) 13W. Rau – IPP AGM 2014

SuperCDMS Soudan – Results and Future BG model predicts ~6 events – BUT: difficult to make good prediction in this low energy range  only set upper limit “Open box”: observed 11 events 3 highest energy events in detector with shorted outer charge channel Probe new parameter space between 4 and 6 GeV/c 2 Incompatible with CoGeNT interpretation as NR signal from WIMPs CDMSlite Lux Standard (high threshold) analysis in progress / additional CDMSlite data collected DM search until fall (expect to be limited by cosmogenic/radiogenic BG by then) Systematic studies until spring W. Rau – IPP AGM 2014

SuperCDMS at SNOLAB Setup for ~400 kg detector mass for later upgrade EURECA indicated interest in contributing additional target mass Shielding includes neutron veto (scintillator) Timing: start construction in early 2015; takes ~2 years to build Funding: $3.4M from CFI / waiting for G2 decision in the US (expected anytime now) 15W. Rau – IPP AGM 2014